In such cases, box filters or Nutsch filters are commonly used for batch filtration. Such filters typically comprise a receptacle in the form of a rectangular or circular drainage plate surrounded by vertical or inclined side walling. A filter medium, usually a filter cloth, lies inside this receptacle, which in use is usually connected downwardly to a vacuum source. A batch of material, e.g. slurry, to be filtered is placed into the receptable and filtration takes place by drainage, usually assisted by vacuum, leaving a filter cake deposited on the filter medium. Frequently this process is followed by cake washing using a suitable wash liquor which drains away and/or is removed by vacuum in the same way.
A disadvantage of this method of batch filtration is the relatively large amount of labour involved in removal of the resulting filter cake by digging it out of the box filter receptable. Such digging also inevitably leads to spillage of some of the cake, which is often a valuable product, and to damage to the filter medium. A further disadvantage is the inability to clean the filter medium effectively between batches, e.g. by washing. Together with the damage to the filter medium caused by the digging out, this leads to a gradual deterioration of filtration rates.
It is an object of the invention to provide batch filtration apparatus which incorporates all the advantages of the stationary manual box or Nutsch filter but enables the cake to be discharged after filtration (and cake washing if appropriate) in a simple, rapid and non-damaging manner and allows the filter cloth to be washed effectively.